In recent years, there have been dramatic improvements in LED technology such that LEDs of increased luminance and color fidelity have been introduced. Due to these improved LEDs and improved image processing technology, large format, full color LED video screens have become available and are now in common use. LED displays typically comprise a combination of individual LED panels providing image resolution determined by the distance between adjacent pixels or “pixel pitch.”
In order to use an LED chip in conventional applications it is known to enclose an LED chip in a package to provide environmental and/or mechanical protection, color selection, light focusing and the like. An LED package also includes electrical leads, contacts or traces for electrically connecting the LED package to an external circuit. In a typical two-pin LED package/component 10, shown in FIG. 25, a single LED chip 12 is mounted on a transparent reflective cup 13 by means of a solder bond or conductive epoxy. One or more wire bonds 11 connect the ohmic contacts of the LED chip 12 to leads 15A and/or 15B, which may be attached to or integral with the transparent reflective cup 13. The reflective cup 13 may be filled with a transparent encapsulant material 16 and a wavelength conversion material, such as a phosphor, can be included in over the LED chip or in the encapsulant. Light emitted by the LED at a first wavelength may be absorbed by the phosphor, which may responsively emit light at a second wavelength. The entire assembly can then be encapsulated in a clear protective resin 14, which may be molded in the shape of a lens to direct or shape the light emitted from the LED chip 12.
The conventional LED package 20 shown in FIG. 26 may be more suited for high power operations which may generate more heat. In the LED package 20, one or more LED chips 22 are mounted onto a ceramic based carrier such as a printed circuit board (PCB) carrier, substrate or submount 23. One or more LED chips 22 may include: a gallium nitride based blue LED chip, a gallium nitride based green LED chips, an AlInGaP red LED chip, a white LED chip, a blue LED chip, a yellow phosphor chip, or a red LED chip. A metal reflector 24 mounted on the submount 23 surrounds the LED chip(s) 22 and reflects light emitted by the LED chips 22 away from the package 20. The reflector 24 also provides mechanical protection to the LED chips 22. One or more wirebond connections 21 are made between ohmic contacts on the LED chips 22 and electrical traces 25A, 25B on the submount 23. The mounted LED chips 22 are then covered with a transparent encapsulant 26, which may provide environmental and mechanical protection to the chips while also acting as a lens. The metal reflector 24 is typically attached to the carrier by means of a solder or epoxy bond.
Conventional LED packages, such as those shown in FIGS. 25 and 26, usually do not have a durable structure that withstands harsh external conditions. When used in LED displays, conventional LED packages present a problem because the LED package is not resistant to water. Accordingly, there is a need for a robust, water resistant, low profile LED device that offers weather resistance for use in outdoor displays and that can be produced with less material at low cost.